1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus which encodes and outputs an image signal which was inputted from an image pickup section.
2. Description of the Related Art
The typical examples for the above-described image processing apparatus are an electronic camera and a video camera. In an electronic camera, the controls such as the shutter speed, focus, zoom, and diaphragm (lens aperture) controls are performed in the lens unit. A gain control is performed in the image pickup section by processing a signal, which was photoelectrically converted and outputted from a CCD. These controls, i.e., the diaphragm and gain controls, are called the automatic exposure control (which is referred to as AE below). The gain control is performed by a voltage control amplifier (referred to as VCA) and clamping circuit (referred to as CL). A video signal which is outputted from the image pickup section is converted to a digital signal by an A/D converter and stored in memory. Then, the digital signal which was read out from the memory is compressed and encoded respectively by a quantizer and coder, and then outputted as coded output.
However, in conventional image processing, the aforementioned controls and the adjustment for the brightness level are complicated which causes the apparatus to be quite large. In addition, since noise removal is not enough, there is the drawback that an efficiency of coding is decreased. A few other drawbacks in the conventional apparatus are further described below.
In an image processing apparatus, which adjusts a brightness level, the following arrangement is well known. First, a video signal is inputted to the A/D converter and converted to a digital signal. The digital signal is stored in the memory. Then, the brightness level which was inputted through a microprocessor (CPU) is added by an adder to every pixel of the video signal which was being stored in the memory. However, since the brightness level needs to be added to each pixel of image data, there are the drawbacks that the number of adding operation is increased, buffer quantity for data which relates to the addition is increased, and the apparatus becomes both complicated and quite large.
FIG. 19 is a block diagram illustrating the arrangement of a conventional electronic camera. The reference numeral 10 is a lens unit comprising a photograph lens, shutter, and diaphragm. The CCD image pickup device 12 converts a subject image picked-up by the lens unit 10 into an electrical signal. The image pickup processing circuit 14 performs a well-known camera signal processing operation such as a gamma correction on the output of the image pickup device 12 and outputs a standard type video signal. The image pickup processing circuit 14 adjusts the gain so that white and black peak levels will be within a predetermined range. The A/D converter 16 digitizes the output of the image pickup processing circuit 14 and the output is temporarily stored in the memory 18. The image data which was read from the memory 18 is either modulated or coded if necessary, and recorded on a recording medium.
The system controller 28 drives a shutter of the lens unit 10 by the shutter drive circuit 30 and also drives a focusing lens and zooming lens by the lens drive circuit 32. Furthermore, the system controller 28 directly controls a diaphragm. Instructions for photographing and the like are inputted to the system controller 28 in a manner such that a user operates the operation section 34. The display section 36 displays the state of operation.
The system controller 28 calculates the white and black peak levels in a screen (or a predetermined area) from the output of the A/D converter 16 (or the memory 18) and controls the gain of the image pickup processing circuit 14 so that the levels will be at a predetermined level.
On the other hand, in an electronic camera which electromagnetically records a still image and a moving image, e.g. an electronic still camera and video camera, the method such that an image is compressed and stored using a recording medium in digital recording has recently been of interest. In this method, because of the digital recording, image deterioration by duplication is decreased and many images can be recorded in a small recording capacity because of compression recording.
However, in the above-described electronic camera in the case of photographing at a low light intensity or at a high shutter-speed, the S/N ratio of the output signal of the image pickup device 12 deteriorates, and if the image is compressed as it is, the quality of the image decreases. Furthermore, there is another drawback such that the compressing efficiency is decreased, since a high-frequency component of an image having a deteriorated S/N ratio is large.
Furthermore, in the case where an image source to be compressed is a reproduction image of a video tape recorder or an output of a TV tuner, the image does not have a sufficient S/N ratio. If such an image is compressed as is, not only is the quality of the image decreased, but also the efficiency of compression is decreased.
As an example, a block diagram of the gain adjustment arrangement in the conventional image processing apparatus is shown in FIG. 20. An analog video signal is inputted to an input terminal and the voltage control amplifier (VCA) 14a amplifies the analog video signal to reach a predetermined white peak level and the clamping circuit 14b clamps a DC level so that the analog video signal reaches a predetermined black peak level.
The output of the clamping circuit 14b is converted to a digital signal by the A/D converter 16 and stored in the memory 18.
The system controller 28 comprising a microcomputer seeks white and black peak levels from the output of the memory 18 and controls the gain of the VCA 14a and the clamping level of the clamping circuit 14b so that the dynamic range of the A/D converter 16 is fully utilized. For example, if the range of the A/D converter 16 is set from xe2x80x9c0xe2x80x9d to xe2x80x9cFFxe2x80x9d (hexadecimal notation), the video signal of white and black peaks shown in FIG. 5A is expanded to the video signal shown in FIG. 5B.
However, in the conventional apparatus, since the white and black peaks are detected from the signal after the A/D conversion, there is a drawback such that the processing of the gain adjustment is susceptible to noise, impulse noise in particular. That is, there is a drawback such that false peak levels are detected and the dynamic range of the A/D converter 16 cannot be efficiently utilized.
This drawback has also arisen when the image data stored in the memory is compressed.
The apparatus which performs AE control is shown in FIG. 21. As shown in the diagram, the image is converted to an electrical signal in the lens unit 10 and the solid state pickup device 12 (which is referred to as CCD below), and then converted to a video signal in the image processing circuit 14. It is further converted to a digital signal in the A/D converter 16 and stored in memory 18. It is then compressed by the image data compressor 20 and the coded output is outputted.
Finally, the AE operation is described. The video signal which was obtained in the CCD 12 and the image processing circuit 14 is converted to a digital signal by the A/D converter 25 through the LPF (low-pass filter) 23 and the SW (switch) 24. Then, the digital signal is integrated by the integrator 26 and inputted into the system controller 28. While the output of the integrator 26 is supervised optimize the inputted light quantity of the CCD 12, the system controller 28 controls an amplifier gain of the iris, or diaphragm, control and image processing circuit 14 and performs automatic exposing.
However, in this conventional apparatus, since the LPF 23, SW 24, A/D converter 25, and integrator 26 are necessary for AE, there are drawbacks that the arrangement of the apparatus becomes complicated resulting in a increased cost.
Accordingly, it is an object of the present invention to provide an image processing apparatus which improves the quality of an inputted image, a pickup image in particular, by a simple arrangement, and also improves the compressing efficiency in a case of compression.
It is another object of the present invention to provide an image processing apparatus capable of high speed adjustment of a brightness level by a simple arrangement.
It is another object of the present invention to provide an image processing apparatus which can be insusceptible to impulse noise of an input signal.
It is another object of the present invention to provide an image processing apparatus which can be insusceptible to a quality deterioration of the input signal.
It is another object of the present invention to provide an image processing apparatus which avoids the deterioration of the S/N ratio and improves the efficiency of compression by a simple construction.
It is another object of the present invention to provide an image processing apparatus which performs the most suitable automatic exposure control by a simple arrangement.
According to the present invention, the foregoing object is attained by providing an image processing apparatus which comprises an orthogonal transformation means, controls an image pickup signal on the basis of various components (e.g. DC component and high-frequency component) outputted from the orthogonal transformation means, and improves a quality of the image by this simple arrangement.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.